The present application claims priority to Japanese Patent Application No. 2001-86838 filed Mar. 26, 2001, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a light scanning apparatus, for example, to a laser scanner constituting a print head of an image forming apparatus such as a laser printer or a digital copier.
2. Description of the Related Art
In the field of laser scanners, conventionally, a technology has been proposed to suppress an optical performance change due to a refractive index change or a configuration change caused by a temperature change, and a performance change due to a mode hop (that is, an oscillation wavelength change) of the laser diode by using a diffracting element as the light source optical system (for example, U.S. Pat. Nos. 6,067,106 and 6,101,020).
It is desirable that the light source optical system used for a laser scanner be made of resin for weight and size reduction. However, in the conventional laser scanners, when the light source optical system is made of resin, the condition for compensating for the performance change due to a temperature change and the condition for compensating for the performance change due to an oscillation wavelength change (that is, axial chromatic aberration) significantly differ from each other, so that performance cannot be maintained.
A principal object of the present invention is to provide a laser scanner being inexpensive and whose performance is stable even when there is a temperature change.
This and other objects are achieved by a laser scanner comprising a laser light source emitting a laser beam; a deflector deflecting an incident laser beam in a main scanning direction; a light source optical system constituted by one optical element made of resin and having: a first transmitting surface on which the laser beam emitted from the laser light source is incident; at least one reflecting surface reflecting the laser beam incident on the first transmitting surface, and having no symmetry axis of rotation; and a second transmitting surface from which the laser beam reflected by the reflecting surface exits, said light source optical system shaping the laser beam emitted from the laser light source into a substantially parallel beam in the main scanning direction, and condensing the laser beam in a vicinity of a deflecting surface of the deflector in a sub scanning direction; and a scanning optical system again condensing the laser beam deflected by the deflector.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.